1. Techinical Field
The invention relates to a device for administering an injectable product in doses.
2. Description of the Related Art
A device such as the invention relates to is known for example from WO 97/36626. The device comprises a casing having a reservoir for the product. A piston is accommodated in the reservoir, said piston forcing product out of the reservoir when moved in a feed direction towards an outlet of the reservoir. A gear rack which presses against the piston moves the piston in the feed direction. The gear rack is provided with rows of teeth. A drive member is further accommodated in the casing, shiftable in and counter to the feed direction relative to the casing, said drive member slaving the gear rack when moved in the feed direction. To this end, the drive member meshes with the rows of teeth of the gear rack via slaving means. To set the amount of product administered in one stroke, the drive member in a front position is manually retracted counter to the feed direction by a set dosage path length. In this way, the slaving means of the drive member slide over the teeth of the rows of teeth and give elastically. The gear rack is prevented from moving back by blocking means accommodated unshiftably relative to the casing. The blocking means co-operate with one of the rows of teeth of the gear rack, such that the blocking means prevent the gear rack from moving counter to the feed direction and allow the gear rack to move in the feed direction by elastically giving.
Correctly and precisely dosing the injectable product is of great importance. Above all in medical technology, the success of a treatment is heavily dependent on correctly dosing the medicine. Precise dosing requires a fine pitch of the previously described gear rack, with small teeth. Moreover, the rows of teeth of a gear rack must satisfy the heavy demands of production
It is the object of the invention to realize a device for administering an injectable product in doses, having simpler components for at least the same functionality.
A device for administering an injectable product in doses comprises a casing having a reservoir for the product, a piston which forces product out of the reservoir when moved in a feed direction towards an outlet of the reservoir, a driven rod which moves the piston in the feed direction, a drive member which may be moved in and counter to the feed direction relative to the casing, said drive member slaving the driven rod when moved in the feed direction, and at least one blocking means which co-operates with the driven rod, such that the blocking means prevents the driven rod from moving counter to the feed direction relative to the casing and allows the driven rod to move in the feed direction.
In accordance with the invention, the driven rod is prevented from moving counter to the feed direction by self-locking. There is a friction lock between the blocking means and the driven rod or a friction lock between the blocking means and the casing. When the driven rod is moved in the feed direction, only the friction lock is overcome. Moving the driven rod counter to the feed direction generates the self-locking of the device via the friction lock, and leads to a friction force which increases with movement of the driven rod counter to the feed direction. A moving force of the driven rod counter to the feed direction thus causes, due to the self-locking of the blocking means, a friction force opposing this moving force which is at least as great. The driven rod can be an easily produced rod made of full material. The use of an internally hollow rod is also possible. A round rod is preferably used. A cornered rod can, however, also be used. The demands of production precision are not heavy. The production costs for such a rod are comparatively low. The term xe2x80x9crodxe2x80x9d in the sense of the invention, however, includes in principle any structure extending in the feed direction which is suitable for transmitting the drive force and absorbing the friction force.
If the driven rod is moved in the feed direction, the friction force existing between the blocking means and the driven rod is overcome. Given a preferably unvarying distance between the driven rod and the casing, the blocking means is not tensed further. The force for moving the driven rod in the feed direction remains constantly low. The blocking means does not block the driven rod against relative movement in the feed direction. The driven rod is able to slide past it.
A spring force is preferably used to generate the friction lock between the blocking means and the driven rod or the blocking means and the casing. The spring force can be transmitted via moving parts of the blocking means onto the point of the friction lock, for example by means of a wedge effect via a plane at an angle to the feed direction. One or more annular spiral springs may for example be used, which press one or more tilting elements distributed evenly around the driven rod against the driven rod or the casing. Springs running radially towards the driven rod or the casing at an angle, which generate the friction lock via pressure parts, would also be conceivable.
Particularly preferably, the blocking means comprises at least one spiral spring or leaf spring. When installed, this spring is deflected from its untensed neutral position and is under bending stress. The friction lock is permanently maintained. The spring can consist of metal, plastic or another suitable material or combination of materials. The spring preferably acts directly on the driven rod or the casing. Particularly preferably, the spiral spring or leaf spring form the blocking means alone.
A spring of the blocking means, or the blocking means as such if it is formed by a spring alone, is arranged in the device such that, due to the friction lock, the blocking means is immediately tensed so heavily between the casing and the driven rod when the driven rod is retracted, that in practice it is not possible to noticeably retract the driven rod in the first place. This is preferably achieved by a form and arrangement of the blocking means which are such that a force acting on the blocking means at the point of the friction lock and counter to the feed direction strives to strain the blocking means perpendicularly to the feed direction. If a force is applied to the driven rod counter to the feed direction, a tendency to move together with the driven rod counter to the feed direction into its untensed neutral position is transmitted onto the blocking means via the friction lock. However, it is not possible for the blocking means to simply return to its neutral position, since in its untensed state the blocking means would protrude out from its fixing point across the distance between the casing and the driven rod. A parallel movement of the side of the blocking means abutting the driven rod or the casing could be achieved by shortening the blocking means in its longitudinal direction. However, this is not possible, since a sufficient rigidity of the blocking means against buckling and straining is ensured. In this state, the blocking means clamps between the driven rod and the casing and thus blocks the driven rod against moving counter to the feed direction. In this way, the clamping force forming the friction lock between the blocking means and the driven rod increases superproportionally with a force acting on the driven rod counter to the feed direction. Movement of the driven rod counter to the feed direction is prevented by self-locking.
In a first preferred embodiment, the blocking means is fixed in the casing or at least connected to it unshiftably in the axial direction. To this end, the blocking means is fixed on one side such that movement relative to the fixing, in or counter to the feed direction, is prevented. The blocking means can be stuck on or shrunk on, however it preferably sits in a groove or other recess. It protrudes via another side in a radial direction towards the driven rod. When installed, the blocking means is held on this side in a position deflected in the feed direction by the driven rod. In this way, it is bent around the fixed side, i.e. its fixing absorbs the bending moment. The blocking means is thus under a bending stress, and the resulting elastic restoring force pushes it against the driven rod.
Equally preferably, the blocking means can be attached, axially unshiftable, to the driven rod. The blocking means and the connection between the blocking means and the driven rod can be realized with the same construction as the connection between the blocking means and the casing described above. It protrudes in a radial direction towards the casing and is held in a position deflected counter to the feed direction by the casing. The elastic restoring force thus generated pushes the blocking means against the casing. The blocking principle here corresponds to the blocking principle in a blocking means connected unshiftably to the casing described above. Due to the then altered geometric relations, the kinematic relations run off inversely. To prevent the driven rod from moving counter to the feed direction, the blocking means is therefore deflected counter to the feed direction in this embodiment variant.
Preferably, a smooth surface of the driven rod or of the casing is ensured at least in the area of the friction lock. The blocking means preferably presses against a smooth surface. This is particularly positive for the dosing acuteness of the device. This further improves the ability to dose progressively.
Preferably, at least two springs form each blocking means. They are installed between the casing and the driven rod on opposing sides or, when a number of springs are used, distributed evenly over the circumference of the driven rod. Each of the blocking means is either unshiftably connected to the casing and deflected in the feed direction or unshiftably connected to the driven rod and deflected counter to the feed direction. In this embodiment, the clamping force of the friction lock is evenly distributed over a number of springs. A large clamping force may be achieved. In addition, the springs can form a guide of the driven rod. If only one spring is to be used, then the force can be absorbed in an opposing abutment. The springs are preferably adapted in their form to the respective pressure surface. When unobstructed, the springs preferably protrude radially from the casing or the driven rod. The inner diameter formed by the springs when unobstructed is smaller than that needed by the driven rod or greater than the inner diameter of the casing, respectively. If the driven rod is installed in the casing, the springs are preferably bent around their fixed sides, are simultaneously tensed in the axial direction and press against the driven rod or the casing.
Particularly preferably, the device additionally comprises at least one slaving means which co-operates with the driven rod and the drive member such that when the drive member is moves in the feed direction, the driven rod is slaved by the slaving means, and the slaving means allows the drive member to move counter to the feed direction relative to the driven rod. In accordance with the invention, a friction lock exists between the slaving means and the driven rod or the slaving means and the drive member, said friction lock causing the driven rod to be slaved by self-locking via the drive member. The slaving means works between the drive member and the driven rod in the same way as the blocking means described above. The design and fixing of the slaving means preferably corresponds to that of the described blocking means. Two alternatives again arise. Either the slaving means is unshiftably connected to the drive member and protrudes in a radial direction towards the driven rod and is held in a position deflected in the feed direction by the driven rod, the elastic restoring force of the slaving means thus generated pressing against the driven rod; or alternatively, the slaving means can be unshiftably connected to the driven rod, protrude in a radial direction towards the drive member and be held in a position deflected counter to the feed direction by the drive member, the elastic restoring force of the slaving means thus generated then pressing against the driven means. With respect to the slaving means, all the embodiments of the blocking means apply analogously regarding its arrangement and function.
The slaving means can, however, also be advantageously installed without the blocking means in accordance with the invention, in a device in accordance with claim 10.